Effects of hypoxia and severity of diabetes on Na,K-ATPase activity and arachidonoyl-containing glycerophospholipid molecular species in nerve from streptozotocin diabetic rats.

The pathogenesis of experimental diabetic neuropathy is associated with the development of endoneurial hypoxia. Exposure of normal rats to hypoxic conditions has previously been shown to reduce nerve conduction velocity. To study the biochemical effects of hypoxia further, streptozotocin-induced diabetic and age-matched nondiabetic rats were maintained in air containing 10% oxygen for nine weeks. As compared to nondiabetic rats kept in room air, sciatic nerve Na,K-ATPase activity was decreased 38% in nondiabetic, hypoxic rats and tended to be lower in diabetic animals maintained in a normoxic environment. However, the enzyme activity was unchanged in diabetic, hypoxic rats, suggesting the existence of an undefined compensatory interaction between these two conditions. Arachidonoyl-containing molecular species (ACMS) of phosphatidylcholine and phosphatidylethanolamine were substantially depleted in nerves from diabetic rats. Hypoxia alone also caused a lesser depletion of some but not all of these ACMS. However, the two conditions together did not produce a further decrease, consistent with the concept that the same mechanism is responsible for loss of ACMS in hypoxia and diabetes. To examine the effects of severity of diabetes on these parameters, groups of rats were injected with either 50 mg/kg or 100 mg/kg streptozotocin. The latter group was maintained by administration of minimal insulin doses and the experiment was terminated after 3 weeks. Serum glucose in rats that received the high dose of drug averaged 12% higher than in the low dose group. As compared to nondiabetic rats, Na,K-ATPase activity was reduced 32-36%, but there was no difference in activity between the two diabetic groups. However, there was a greater loss of ACMS in the more severely hyperglycemic rats. In rats that received comparable streptozotocin doses, measurement of ACMS depletion after 3, 9 and 32 weeks of diabetes revealed the loss is progressive with time. Thus, glycerophospholipid ACMS is a sensitive index of the severity and duration of experimental diabetic neuropathy.